Protection of a die surface from access by unauthorized personnel has been in the past limited to various assembly techniques that make access to the surface of the die difficult. Die coatings that obscure the surface of the die have been used in the past to both hide and protect the surface from attack. There have been some attempts to embed a physical mesh into the coating to deter access, but this mesh is neither active nor self checking.
Die coating and assembly techniques along with an applied static mesh are passive deterrents to attackers, who are trying to reverse engineer, or gain information from devices. While each technique has advantages, one disadvantage is that there is no capability to detect an attack and have the device react to that attack during chip operation. The static nature of the protection allows attackers to attempt to compromise the device security during operation and gain information.
Attackers with access to ion-milling/e-beam equipment are able to etch/grind down through protective coatings, re-stitch damaged bonds and then ion-mill (drill) into the surface of the device and e-beam probe signals within the device. Detection of the physical intrusion into the die surface requires deterring and detecting this form of attack.
Ion-milling is capable of drilling into the surface of the insulating layers to access wires running below the surface. By depositing metal, it is possible to bring buried signals running on these wires to the surface of the die. These signals may be measured with an e-beam probe or may be connected to some other signal on the die.
As will be explained, the present invention advantageously embeds a physical mesh into a die surface during the manufacturing process to deter unauthorized access. In addition, the physical mesh provides active, self checking of an attack to the die surface.